1. Field of Invention
This invention relates to a high security lock, and more particularly to an improved high security lock with time delayed activation, with defeat and automatic reset characteristics.
2. Description of the Prior Art
The use of high security, low cost locking devices are currently in demand in the coin-operated machine industry for use in vending machines, washing machines, and the like. Due to the high rate of theft and pilferage in such machines the locks used to secure the coin deposit must be made as secure as possible, while the total cost of such a high security lock must be limited to that commensurate with the value of the money secured. More recent high security locking devices are of the electromagnetic combination type as opposed to the conventional, pick-proof, pin-tumbler locks. One such electromagnetic high security lock is disclosed by J. R. Dettling in U.S. Pat. No. 3,873,892, entitled HIGH SECURITY LOCK, and owned by the common assignee. The high security lock disclosed by Dettling is comprised of a lock portion and a separate, removable magnetic key portion. The lock portion is unlocked through activation of magnetically operable switches in response to the presentation of a predetermined unlocking combination code signal from the magnetic key. The security lock includes circuitry for defeating the unlocking function in the event of an improper placement of the magnetic key to the surface of the lock portion, however once proper placement of the key and entry of the determined unlocking combination code is made, the unlocking function is immediately activated. Admittedly, the requirements that the unlocking function may only be performed by presentation of the determined unlocking combination code by a magnetic key properly placed on a defined surface of the lock do provide a significant deterrant to unauthorized entry, however, the imaginative efforts of a thief are boundless. One significant limitation to the security of the lock is the immediate activation of the lock which aids unauthorized entry through a "searching combination" technique, i.e. successive key placement and combination code setting permutations. A proper key placement and combination code is signalled by the audible sounds provided by the electromotive unlocking device. Therefore, to further improve the security of the locking device, it is desirable to provide delayed activation of the lock to further reduce the probability of unauthorized unlocking of the device through a "searching combination" technique, while maintaining the low cost of the device.